Feeding Difficulties

[Stormlantern]

Hoping for some wisdom from the more seasoned cephalopod keepers here.

I have a dwarf octo who's been in my tank since February (see thread Suspected Mercatoris (and if so..) but hasn't been out much lately. That is, I haven't seen "him" beyond one or two arms for over a month. He doesn't leave the one cave in the live rock, so I'm pretty clueless as to sex or species (he is just more convenient for me than "it" and I liked the name Marcus)
My main concern is feeding. I've tried several different foods, listed below, with no consistent success. As far as I can tell, he's still quite small (my guess on mantle length would be <1 inch) but I haven't seen the whole body since March so that's just a guess. What foods are good for a tiny, picky octo?
List of tried foods:
-frozen krill (usually rejects)
-frozen clam (usually rejects)
-frozen scallop piece (usually rejects)
-frozen squid piece (sometimes accepts)
-frozen crabmeat piece (sometimes accepts)
-frozen brine shrimp (only tried once. Forceful rejection via siphon)
-live ghost shrimp (never catches)
-speared ghost shrimp (sometimes accepts)
-smallest fiddler crab I could find ~2cm across carapace, (never caught, found dead in tank)
-small emerald crab with snipped claws ~1.5cm across carapace (lost in tank, still alive as of 3 days ago)
-small sally lightfoot crab ~2cm across carapace (still happy and active in the tank)
-red legged hermit crabs (initially ate several but the 5-6 that are left seem unperturbed, and have been for some time)
I've been feeding in the evening, usually sometime between 8:30 and 10:00. i've offered food at various times (7am, 1pm, 2am) but have only seen him during the evening.

I'm also still nursing the hope I can get the little guy to interact. Is there a way to warm up to being out in the open, at least once in a while? And maybe move to games or petting?

One obstacle I have is the tank itself. It's a 90 gallon hex, and I have trouble reaching down the 30 inch height to get close to the "lair rock" even with a bamboo skewer. I've been thinking about switching to a different setup, and I found a good offer for a used 75 reef ready that's only 18" tall, so maybe that would improve ease of access. Although then I'd have to octo-proof again I had 3 peppermint shrimp in with him, but they seemed aggressive and I took them out, hoping that he would feel braver without shrimp twice his size bobbing side to side next to his lair. Still have a brittle star, sea urchin and sand sifting star, as well as the crabs that were not consumed as I had hoped.

Let me know what thoughts you have, and any advice.
Thank you!!

 

[DWhatley]

I've never had a lot of success feeding O. mercatoris much other than impaled shore shrimp and live fiddler crabs but was amazed to find our last couple WOULD take thawed table shrimp IF offered in pea sized chunks.

O. mercatoris is likely the least interactive of the species I have kept. I did have one exception but his interaction was food driven and not curiosity about his food slave (he was still a favorite though).

IME, female mercs will find a den and rarely leave where males will change dens from time to time. However, since you have had this one since Feb and are now seeing less of it in the last months, I suspect she may be brooding. Dwarf species typically only live for between 8 and 10 months (I have had some to live over a year but others in the same hatching only 8 months)